"He's going to have a second act unlike any writer in history," said Shane Salerno, who has written the biography. "There's no precedent for this." In an interview earlier this year, Salinger's son, Matthew, said he was sceptical that the biography and an accompanying documentary film would deepen public understanding of his father, who, he said, had confined his intimate dealings to a circle of seven or eight people for decades.

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Mr Salerno, a filmmaker, is convinced his book and film will shed further light on the New York-born writer.

He spent nine years researching Salinger and analysed hundreds of previously unpublished photographs and letters.

Among the documents that he studied was a Second World War diary that belonged to one of Salinger's lifelong friends, a fellow soldier named Paul Fitzgerald, who is now deceased.

"If that's not the inner circle, I don't know what is the inner circle," said Mr Salerno. He added that his understanding of the publishing plans took shape "fairly late" in his research for the 700-page biography.

Salinger's widow and son, who run the writer's estate, have remained silent since his death, and no one outside the family circle knows what the late author's house in Cornish, New Hampshire, contains.

Mr Salerno and his co-author, David Shields, claim Salinger prepared for a series of works to be published posthumously. They said the books would be made public between 2015 and 2020, but did not say who would publish them.

One collection, to be called The Family Glass, would add five new stories to an assembly of previously published tales about the fictional Glass family, who featured in Salinger's Franny and Zooey and elsewhere.

Another book would include a retooled version of a known but unpublished tale, The Last and Best of the Peter Pans, to be collected with new stories and existing works about the fictional Caulfields, including The Catcher in the Rye.

The works are said to include a story-filled "manual" of the Vedanta religious philosophy, with which Salinger was involved, a novel set during the Second World War and based on his first marriage, and a novella modelled on his war experiences.

Salinger never authorised a biography, but several unauthorised books have come out over the past 30 years, notably one by Ian Hamilton.

In 1987, Salinger blocked the release of Hamilton's JD Salinger: A Writer's Life, citing the use of previously unpublished letters.

The new biography, Salinger, portrays the writer as deeply traumatised by his war experiences and stunned by his fame as an author. He also is painted as less reclusive and detached than previously suggested.

The film is due to be released in the United States next month, to coincide with the publication of the book.